A fuel cell system is increasingly being used as a power source in a wide variety of applications. The fuel cell system has been proposed for use in vehicles as a replacement for internal combustion engines, for example. The fuel cell system may also be used as a stationary electric power plant in buildings and residences, portable power in video cameras, computers, and the like. Typically, the fuel cell system includes a plurality of fuel cells arranged in a fuel cell stack to generate electricity, which is used to charge batteries or provide power to an electric motor.
A typical fuel cell is known as the polymer electrolyte membrane (PEM) fuel cell, which combines a fuel such as hydrogen and an oxidant such as oxygen to produce electricity and water. The oxygen is generally supplied by an air stream. In order to perform within a desired efficiency range, a sufficient humidification of the polymer electrolyte membranes of the fuel cell should be maintained. The sufficient humidification desirably extends the useful life of the electrolyte membranes in the fuel cell, as well as maintains the desired efficiency of operation.
As part of the fuel cell system, a water vapor transfer (WVT) device may be employed to humidify the air stream entering the fuel cell stack. The WVT device transfers water vapor from an exhaust stream from the fuel cell stack to a feed stream entering the fuel cell stack. This is generally accomplished by using a water vapor transfer membrane which allows only water vapor to pass therethrough. This membrane may be permanently attached to a diffusion media layer, called a separator, which controls gas flow. The locations where the membrane is attached to the separator are desirably leak free.
An exemplary water vapor transport device for a fuel cell system is disclosed in U.S. Pat. Appl. Pub. No. 2009/0092863 to Skala, the entire disclosure of which is hereby incorporated herein by reference. Skala describes a plate for a water vapor transport device having a top layer formed from a diffusion medium and a bottom layer formed from a diffusion medium. An array of substantially planar elongate ribbons is disposed between the top and bottom diffusion medium layers. A membrane is adhered to at least one of the top and bottom diffusion medium layers.
It is also known to manufacture a water vapor transfer separator consisting of a plastic plate with flow channels either machined or molded into the plastic plate. The gas diffusion and membrane layers are attached to the plastic plate using pressure sensitive adhesive (PSA). However, the PSA is difficult and time consuming to apply. Additionally, where the PSA has not been applied correctly, the resulting water vapor transfer device generally cannot be repaired.
There is a continuing need for a manufacturing system and method to efficiently and permanently bond water vapor transfer membranes to gas diffusion separators. Desirably, the manufacturing process creates a durable, leak free bond between the water vapor transfer membranes and the separators, produces an assembly which meets dimensional and flatness tolerances in specific areas without adversely affecting the water vapor transfer rate of the resulting water vapor transfer device, and can be readily incorporated into either a roll-to-roll process or a batched sheet process.